The present application relates to a method of forming a semiconductor structure and, more particularly, to a method of forming source/drain metal semiconductor alloy contacts that have increased contact area.
Field effect transistors (FETs) are the basic building block of today's integrated circuits. Such transistors can be formed in conventional bulk substrates (such as silicon) or in semiconductor-on-insulator (SOI) substrates. State of the art FETs can be fabricated utilizing a gate-first process or a gate-last process. In a gate-first process, a gate material stack is first formed, followed by the formation of source/drain regions. In a gate-last process, the source/drain regions are formed prior to replacing a sacrificial gate structure with a functional gate structure.
State of the art FETs can be fabricated by depositing a gate conductor over a gate dielectric and a semiconductor substrate. Generally, the FET fabrication process implements lithography and etching processes to define the gate structures. After providing the gate structures, source/drain extensions are formed into a portion of the semiconductor substrate and on both sides of each gate structure by ion implantation. Sometimes this implant is performed using a spacer to create a specific distance between the gate structure and the implanted junction. In some instances, such as in the manufacture of an n-FET device, the source/drain extensions for the n-FET device are implanted with no spacer. For a p-FET device, the source/drain extensions are typically implanted with a spacer present. A thicker spacer is typically formed after the source/drain extensions have been implanted. In some instances, deep source/drain implants can be performed with the thick spacer present. In other instances, and for advanced technologies, the source region and the drain region can be formed using a selective epitaxial growth process. High temperature anneals can be performed to activate the junctions after which the source/drain and top portion of the gate are generally converted into a metal semiconductor alloy (i.e., a metal silicide). The formation of the metal semiconductor alloy typically requires that a transition metal be deposited on the semiconductor substrate followed by a process to produce the metal semiconductor alloy. Such a process forms metal semiconductor alloy contacts to the deep source/drain regions.
In current technologies and for tightly spaced devices, the contact area for metal semiconductor alloy formation above the source/drain regions is extremely limited. As such, there is a need for providing a method in which source/drain metal semiconductor alloy contacts can be formed that overcomes the drawbacks associated with conventional processes.